This double-blind study will compare the efficacy and safety of oral 256U87 with acyclovir for the treatment of herpes zoster in immunocompetent adults who are 50 years of age or older. Otherwise normal adults with localized herpes zoster presenting within 72 hours of the onset of vesicles will be randomized to three groups: 256U87 1000mg orally tid X 7 days; 256U87 1000mg tid X 14 days; and acyclovir 800mg 5 times a day X 7 days. Patients will be evaluated for a total of six months.